1. Field of the Invention
The present invention relates to a radiation image processing device and method and a radiographic imaging system. More particularly, the present invention relates to a radiation image processing device and method and a radiographic imaging system, in which an exposure field is automatically set in the course of imaging, and in which a display image suitable for image interpretation can be obtained in a simple structure.
2. Description Related to the Prior Art
An X-ray imaging system or radiographic imaging system in which X-rays are used is well-known in the field of medical diagnosis. The X-ray imaging system includes an X-ray source apparatus or radiation source apparatus, and an X-ray imaging apparatus or radiographic imaging apparatus. The X-ray source apparatus generates X-rays. The X-ray imaging apparatus forms a radiation image or X-ray image by detecting X-rays transmitted through a body of a patient. The X-ray source apparatus includes an X-ray source, a controllable source driver and a radiation switch. The X-ray source emits X-rays to the object. The source driver controls operation of the X-rays source. The radiation switch sends an input signal to the source driver for starting the X-ray source. The X-ray imaging apparatus includes an electronic cassette or X-ray image detector, and a console structure. The electronic cassette detects the radiation image according to X-rays from the object. The console structure controls the electronic cassette, processes the radiation image for image processing, and performs storing processing and display processing of the radiation image.
The electronic cassette has a sensor panel or sensor matrix, which is referred to as an FPD or flat panel detector, and detects the radiation image electronically. An active pixel area of the sensor panel includes a great number of pixels for storing signal charge according to a dose of incident X-rays. Each of the pixels includes a photoconductor for generating and storing charge, and a switching element such as a TFT. In case the switching element is turned on, the sensor panel reads out the signal charge into a signal processing circuit from the photoconductor of each pixel through a signal line disposed for each of arrays of the pixels. The signal processing circuit converts the signal charge into a voltage signal to detect the radiation image electrically.
In the X-ray imaging system, the use of AEC (automatic exposure control) is known. For the purpose of forming the radiation image with an appropriate quality with a reduced dose of X-rays to the object or a body, a dose of X-rays is detected during irradiation of the X-rays, to stop the irradiation of the X-ray source upon reach of a cumulative dose of X-rays to a target dose. The cumulative dose of the X-rays from the X-ray source is determined according to a tube current-time product (in the unit of mA·s) obtained by multiplication of irradiation time of X-rays by a tube current determining the dose of X-rays per unit time. In general, each of imaging conditions including the irradiation time and tube voltage has recommended values with differences in compliance with body parts, sex, age and other specifics of a body or object, the body parts including a chest, head and the like. However, the use of AEC is important for obtaining improved image quality because transmittance of X-rays differs according to specificity of the body, for example, a body size.
A monitoring device or AEC device for detecting a dose of X-rays transmitted through an object is used for the AEC. A known example of the monitoring device is an ionization chamber for combined use with the electronic cassette. The ionization chamber includes monitoring sensors, two of which are disposed at two upper points in compliance with right and left lungs in imaging of the chest, and one of which is disposed under the two upper points. The ionization chamber is so disposed as to cover a front or rear surface of the electronic cassette. For example, the upper two of the monitoring sensors are selected as an exposure field (receiving field) as a reference of monitoring in the AEC before the imaging of the chest. Then the object is positioned for relative positioning with the electronic cassette to oppose the right and left lungs of the body to the selected exposure field. Assuming that the positioning is incorrect, the AEC cannot be performed correctly due to an offset between the right and left lungs and the exposure field. The positioning must be exact. After completing operation of the positioning, the imaging is started. In the imaging, a time point of stopping irradiation of X-rays is obtained according to a dose signal output by the monitoring sensors selected as the exposure field.
JP-A 7-201490 and JP-A 2002-000590 disclose a structure including the sensor panel and the monitoring device combined with the sensor panel. The sensor panel of the documents has pixels which operate as the monitoring sensors within the active pixel area for detecting the radiation image. Any of the pixels can be manually designated as the exposure field. For the AEC by use of the monitoring in the sensor panel according to this disclosure, the exposure field is selected prior to the imaging and an object is positioned in compliance with the selected exposure field, in a manner similar to the use of the ionization chamber. Then the imaging is started.
Automation of setting the exposure field in the course of imaging has been technically conceived as a development of the disclosure in JP-A 7-201490 and JP-A 2002-000590 in which pixels of the sensor panel are used as the monitoring sensors. Part of the pixels in the sensor panel are used as monitoring pixels for operation as the monitoring sensors. The monitoring pixels are arranged within the active pixel area in a discrete manner. The exposure field is determined according to the dose signal output by the monitoring pixels. For example, one of the monitoring pixels opposed to the right and left lungs in the chest imaging generates a higher output than those opposed to other body parts adjacent to the right and left lungs. Thus, the monitoring pixels with the higher output than the other monitoring pixels are automatically set as the exposure field. Then the monitoring pixels of the exposure field are used for the AEC according to the dose signal. As a result, it is technically unnecessary to select the exposure field conventionally required for preparatory operation. Also, strictly high precision in the positioning of the object is unnecessary because the exposure field is automatically set according to the relative position between the object and the electronic cassette.
In image diagnosis of the medical field, a plurality of the radiation images formed by imaging the same body part in plural events with a time interval is read and interpreted in comparison as observation of the progress, for example, images before and after surgery. The radiation images are arranged and displayed in a screen view of a display panel, or displayed respectively in a manner changeable over one after another. The radiation images are displayed suitably for image interpretation in comparison.
For example, an object in the radiation image before surgical operation is disposed approximately at the center. However, the object after the surgical operation may be offset toward the right or left in the radiation image. The image interpretation in comparison is difficult upon occurrence of a change in the position of the object between the plural radiation images. It is preferable that a position of the object in the radiation images is constant between the radiation images for use in the observation of the progress.
Assuming that the automated setting of the exposure field in the course of imaging is used, no precision in the positioning the object in the conventional technique is necessary. However, a relative position between an object and the electronic cassette is unequal between images obtained from plural events of imaging for the purpose of the observation of the progress. A problem arises in a difference in the position of an object between the radiation images.
To cope with this problem, the radiation images are analyzed in image analysis such as pattern analysis to recognize a position of the object in the radiation images. Position matching is performed to match the position of the object between the radiation images according to the recognized position. However, the image analysis method of recognizing the position of the object in the radiation images requires complicated processing and long time. There is no known solution of a simple form in relation to the above-described problem.